Owing to the length necessary on account of their tandem cylinders and to the excessive stresses to which they are liable from the nature of their working cycle, gas engines in large sizes for the iron and steel industries have never been built except as horizontals, therefore the number of types is very much more limited than is the case with steam blowing engines.

The first installation of gas blowing engines on a large scale in this country was that of the Lackawanna Steel Company at Buffalo, which was started about 1903-04, and has been the bone of many bitter arguments pro and con oh the whole gas engine situation and on the particular type of engine installed. These are two-stroke cycle engines built under the Koerting patents.

They have a single double-acting cylinder on each side and every alternate stroke is a working stroke exactly as in the steam engine, their gas and air being supplied them by large pumps driven by cranks on the ends of the main shaft, one of which supplies the gas, the other the air, not only for combustion, but also for scavenging the cylinder of the burnt gases from the last stroke. This is done by a "plug" of air which is driven through the cylinder behind the burnt gases and in front of the fresh charge, and to a great extent prevents the mixing of these, which would greatly reduce the efficiency.

No exhaust valve is used. The piston uncovers an annular port in the cylinder near the end of its stroke and the burnt gases and plug of scavenging air escape through this while it is uncovered. During the latter part of this interval the fresh charge is introduced into the rear end of the cylinder, but is prevented from escaping by the air plug.

This engine then, avoids the necessity of having two cylinders to make each stroke a working stroke and avoids the exhaust valves of the four-stroke cycle, but does so at the price of two large crank-driven pumps which have to raise the charge to higher pressures to force it into the cylinder than are necessary in the four-stroke cycle. In addition to this the air required merely for scavenging, must be handled and compressed. These engines after more than ten years of continuous service are still in regular operation and, although steam blowing engines are installed, they are held in reserve and the gas engines run by preference not only of the mechanical department, but also of the furnace manager, because they are not only more economical but require less attention and repairs than the steam engines.

The gas-cleaning installation at this plant is almost rudimentary as compared with more modern ones and the resulting gas much less clean, yet these engines are operating successfully with the original cylinders in some cases without even being bored out and lined, with some of the original piston rods, and almost all the original pistons.

These engines have horizontal gas cylinders and vertical air cylinders concerning which construction no more need be said than was said concerning the steam engine of that type, except that the high speed and great inertia of the reciprocating parts of the gas engine makes it even more unnecessary than in the steam engine, and it has not so far as I know been used in any other large installations of gas blowing engines in America.

Judged by the test of time and service this installation must be judged as great a success as an initial installation of any kind ever is. It was described in much detail by Mr. E. P. Coleman in Vol. XXXII of the Transactions of the American Society of Mechanical Engineers, in which excellent article the statement is made that these engines require about 18,500 B.t.u. per indicated horse-power in the air cylinders, an efficiency of 13.7 per cent.

Recent types of four-cycle engines at three-quarter load give about 22 per cent. efficiency at the shaft and reducing this by 10 per cent. we get 20 per cent. as the efficiency based on the indicated horse-power in the air cylinder or nearly one-half more than of the Koerting engines, so the reason for the exclusive use of the four-cycle type is not far to seek. At the same time these four-cycle engines represent a much more recent state of development than do the Lackawanna engines and it is claimed that the later examples of this Koerting type in Europe give far better results than do the earlier ones. Still it must be acknowledged that while many attempts have been made to improve the economy of the two-cycle engines for all uses and in all sizes none of these attempts have ever succeeded in putting it in the same class for economy as the four-cycle, and it may now probably be said with safety that there are fundamental obstacles to success in this endeavor, which will never be overcome.

Fig. 116 shows a gas blowing engine built by the William Tod Company with twin tandem gas cylinders on one side of the crankshaft and a blowing cylinder on the other side, driven by stretcher rods as described for the inside crank steam engine. This construction is no shorter than that of a straight tandem engine, and as the piston rods pass through the cylinder heads, and are supported by slides outside them in all cases, I do not fully understand the advantages of this construction, but it is in extensive use and seems to give good satisfaction.

Fig. 117 shows a similar design of engine built by the Allis-Chalmers Company, and Fig. 118 shows one of the largest installations of gas blowing engines in this country, also built by the Allis-Chalmers Company.

Fig. 117. Allis-Chalmers 44 x 60 twin tandem gas engine with 60 X 60 air cylinders.

Fig. 119 shows in outline a straight tandem gas blowing engine built by the Mesta Machine Company with the crankshaft at one end, the blowing cylinder at the other, a design which I prefer to the inside crank type.

Fig. 118. Row of eight Allis-Chalmers gas blowing engines.

All these engines are of the four-stroke cycle, double-acting, double-tandem type with admission valves and exhaust valves all in the central vertical plane to give maximum accessibility without the necessity of removing cylinder heads and to avoid the formation of pockets in the cylinder heads.

The details of the designs differ but not very much more than the details of steam engines.

The air cylinders do not differ from those of steam engines except that the speeds at which they are required to run average higher and the valves must be designed to meet this condition.